If solubility of KCl at a particular temperature is 25g/100g of water, then on adding 60 gm of KCl to the same volume at same temperature, the salt that remains undissolved is

Mass of KCl in 100 g of water in saturated solution = 25 g 

For 60 g of KCl, the mass of salt dissolved = $\frac{25}{100}\times 60=15 \mathrm{g}$

Mass of undissolved salt = 60 - 15 = 45 g

Therefore the correct option is B) 45 g.